The present invention relates generally to reciprocating piston compressors for compressing fluid and, more particularly, to such compressors having a cantilevered suction leaf valve, wherein a positive stop is provided in the top surface of the crankcase to limit the travel of the unattached end of the suction valve when the valve opens during an intake stroke of the compressor.
In a typical reciprocating piston compressor, a cylinder is defined by a compressor crankcase and a piston reciprocates within the cylinder to compress gaseous refrigerant therein. In a compressor to which the present invention pertains, a valve plate assembly is disposed intermediate the top surface of the crankcase and a cylinder head mounted thereto. The valve plate assembly includes a suction valve operable to permit fluid into the cylinder during an intake stroke of the compressor, and a discharge valve operable to exhaust fluid into a discharge space defined by the cylinder head during a compression stroke of the compressor.
With respect to the aforementioned valve plate assembly, a valve plate covers the cylinder and includes a suction inlet port extending therethrough to provide fluid communication between the cylinder and a suction pressure chamber in the cylinder head. A cantilevered suction leaf valve, also known as a "flapper" valve, is mounted adjacent the cylinder-facing side of the valve plate. An unattached end of the valve is in registry with the suction inlet port of the valve plate. During the compression stroke of the compressor, the unattached end is forced by pressure to sealingly cover the suction inlet port. During the intake stroke of the compressor, the unattached end is forced away from the valve plate by fluid being drawn through the suction inlet port.
In order to prevent overstressing and resulting fatigue of the suction leaf valve caused by bending during the intake stroke of the compressor, the unattached end of the valve is typically limited in its travel into the cylinder by engagement with a positive stop milled in the crankcase. For instance, the positive stop of the prior art comprises a flat-bottomed, crescent-shaped step that is end mill cut to a depth below the top surface of the crankcase and intersects the cylinder wall, as shown in FIG. 7.
While, the flat-bottomed positive stop of the prior art is generally effective in limiting the movement of the unattached end of the valve into the cylinder, several problems may be identified. For instance, the entire portion of the unattached end that contacts the flat bottom of the positive stop strikes the bottom surface simultaneously at high velocity. This results in excessive stress on the suction valve, which may reduce the life of the valve. Also, the impact of the contacting portion of the unattached end against the flat bottom of the positive stop may produce undesirable valve noise.
Reexpansion volume is a condition universally associated with and affecting the operating efficiency of reciprocating piston compressors, particularly smaller refrigeration type compressors. Generally, reexpansion volume is the volume remaining in the cylinder when the piston is at top dead center. Fluid occupying the reexpansion volume is compressed and expanded during each work cycle without producing an appreciable benefit. Accordingly, it is desired to minimize the reexpansion volume in a reciprocating piston compressor. To this end, specially designed pistons, valve plates, and valving have been developed to minimize reexpansion volumes.
The present invention is directed to overcoming the aforementioned problems associated with reciprocating piston compressors having cantilevered suction leaf valves and positive stops to limit the movement of the unattached ends thereof, wherein it is desired to reduce stresses on the suction valve and minimize reexpansion volumes in the cylinder.